1. Field of the Invention
The present invention relates generally to implants, and in particular to a porous implant system and treatment methodology for both orthopedic and soft tissue applications, which promotes tissue interdigitation and healing.
2. Description of the Prior Art
In the medical, dental and veterinary fields, implants are in widespread use for treating a variety of patient conditions. For example, in the field of orthopedics, joints are commonly replaced with implants after the original joints fail through degeneration, trauma and other causes. Such implants are typically designed to promote bone induction, bone replacement and soft tissue anchoring. Porous materials have been extensively used in the manufacture of joint prostheses for this purpose. Their open-lattice configurations tend to promote interdigitation, tissue ingrowth and tissue outgrowth whereby integration with the patients' living tissues can occur.
Trabecular metal comprises a type of porous material, which is commonly used in orthopedic procedures. An example of such an implant is described in U.S. Pat. No. 5,456,723 entitled “Metallic Implant Anchorable to Bone Tissue for Replacing a Broken or Diseased Bone”. Porous thermoplastic materials have also been used for orthopedic implants. Examples are described in U.S. Pat. No. 4,164,794 and No. 4,756,862, both of which are entitled “Prosthetic Devices Having Coatings of Selected Porous Bioengineering Thermoplastics”. U.S. Pat. No. 5,443,512 for “Orthopedic Implant Device” and No. 6,087,553 for “Implantable Metallic Open-Celled Lattice/Polyethylene Composite Material and Devices” both describe orthopedic implants with metal and plastic composite constructions. All of these patents are incorporated herein by reference.
Trabecular metal and other porous implant materials, including thermoplastics, can promote tissue ingrowth under certain conditions. However, the depth of penetration of bone and soft tissue ingrowth may be limited by various biological factors. Moreover, depth and quality of tissue penetration, and the physical properties of the host/prosthesis interface, may be limited by both pathological and physiological host factors.
Another persistent problem with such implants relates to the potential for infection. Porous materials tend to encourage tissue ingrowth, but they can also accommodate microbes and metabolic agents. Digitization and integration can be hindered by the presence of toxins, wound drainage fluid and other substances, particularly when they are trapped in the porous material and closed within a surgery site after a medical procedure.
Artificial joints, implants and other prostheses are further susceptible to persistent problems with secure bonding to patients' living tissue. Macro and micro motion in such connections can compromise replacement joints and cause their premature failure. In order to strengthen such connections, adhesives and cements have been developed for bone-to-implant bonds. Such adhesives and cements can be combined with antibiotic and antimicrobial agents. For example, ALAC identifies an acrylic cement loaded with antibiotic or antimicrobial agents (ABX). Polymethylenemethacralate (PMMA) cement is also used for this purpose. However, problems can be encountered with inducing such cements into the voids and latticework formed in the porous implant materials.
In the related fields of chronic wound care and post-operative incision healing, gradients of various kinds have been utilized. For example, thermodynamic (temperature) gradients can stimulate cell growth. Electrical, gravitational and magnetic fields have also been utilized for this purpose. Considerable research is currently being directed toward the use of biologics in various medical applications. Gradients can be established with biological agents for enhancing healing and countering infection. Pressure differentials and gradients have been applied to close separated tissue portions and promote their healing. Negative pressure gradients have been used to apply suction forces for draining bodily fluids and exudates. Positive pressure gradients have been used to irrigate wound sites and infuse them with pharmacological agents, such as antibiotics, growth factors, etc.
The present invention combines concepts from the porous implant field with gradient formation equipment and treatment protocols to promote tissue ingrowth for anchoring implants. Forming a gradient at a situs also facilitates drainage and the application of biologics, such as antibiotics, growth factors and other fluids for controlling infection and promoting healing.
The design criteria for implants include secure connections with living tissue, facilitating tissue ingrowth, infection resistance and permanency. Another design objective is applicability to a wide range of procedures, including prosthetic fixation, cosmetic and structural bone substitution, treatment of failed bone unions, bone defects, composite tissue defects and other conditions. Heretofore there has not been available a porous implant system and treatment method with the advantages and features of the present invention.